Water mixing valves are widely used to control the flow of water discharged from bathtub spouts and shower heads. The popularity of mixing valves for such applications is due in large part to their simplicity and economy of design and construction, as well as quick familiarity and ease of operation by the user. As used in the trade, the term "mixing valve" refers to a valve connectable to sources of hot and cold water and which has the capability of being adjusted to vary the proportions of hot and cold water in the water flow passing through the valve. Mixing valves do not have the capability of controlling the volume of flow passing therethrough, but often are marketed and installed in conjunction with a second valve that performs the volume control function. An example of such a product offered commercially may be seen disclosed in U.S. Pat. No. 3,192,939, issued July 6, 1965.
Mixing valves have a single operating handle that manually can be rotated (most commonly counterclockwise) from an off position wherein no water passes through the valve, through various intermediate positions wherein cold water only or cold-hot water mixtures are passed, to a full on position passing only maximum temperature hot water through the valve. It is apparent that such an arrangement admits to the possibility of inadvertent or unintentional handle positioning in the full on, maximum temperature position due to accidental user contact with the operating handle or unfamiliarity with the temperature of water discharged at various handle positions. Discomfort or even injury to the user can result from such a situation.
In the past, mixing valve designs have been advanced including provisions to prevent unwanted operating handle positioning at high temperature settings. An example of such a design is disclosed by U.S. Pat. No. 3,011,520, issued Dec. 5, 1961. To my knowledge, such designs have not achieved commercial popularity, due possibly to design complexity adding substantially to the manufacturing costs of the mixing valve and/or inconvenience of operation of the anti-scald mechanism.
It is, therefore, an object of this invention to provide anti-scald apparatus for a water mixing valve that minimizes the possibility of undesirable discharge of high temperature hot water to the detriment of the valve operator. A further object of this invention is the provision of a design for such apparatus that allows economy and ease of manufacture of parts and assembly, with a minimum of tooling changes over the tooling used to manufacture similar mixing valves not including such apparatus. A still further object of this invention is the provision of mixing valve anti-scald apparatus of simple configuration with few moving parts that it is reliable in operation over the life of the mixing valve and provides easy familiarization of operation to the valve operator.